A roller cone rock bit is a cutting tool used in oil, gas, and mining fields to break through earth formations to shape a wellbore. In shaping the wellbore, the roller cone bit drills through different geological materials making up different rock formations. Although the drill bit encounters different formations at different depths in drilling through rock, generally speaking all parts of the drill bit are drilling the same type of rock formation at the same time.
In hydraulic fracturing operations, a frac plug is secured to a casing that lines the borehole. The frac plug is something of a disposable tool because after the frac plug has performed its function, it is drilled out using a roller cone rock bit manufactured to International Association of Drilling Contractors (IADC) standards, and the drilled out pieces of the plug are flushed up the wellbore by the drilling mud. A frac plug is a generally cylindrical component formed of different materials disposed at different radial positions moving from a generally hollow center. In contrast to drilling through rock formations, when drilling out a frac plug, the drill bit simultaneously drills through different materials. The different materials create different penetration efficiencies and wear characteristics on different parts of the bit.
Reference is made to U.S. Pat. No. 5,131,480 to Lockstedt (the disclosure of which is incorporated by reference), which discloses a milled tooth rotary cone rock bit where a heel row of each cone is relieved and tungsten carbide chisel inserts are inserted in the relieved heel row. The heel row inserts cooperate with the gage row milled teeth and progressively cut more of the gage row of the bore hole as the gage row milled teeth wear.